This invention relates to a larynx stroboscope device for observing and diagnosing vocal cords which make voice emissions. As is well known in the art, a larynx stroboscope is a device that operates to cause a discharge tube to emit light in synchronization with the vibration of the vocal cords which are making voice emissions and to apply the light to the vocal cords. Hence, the observer can observe the vocal cords as if they were at rest. In addition, the observer can observe the stationary image of the vocal cords in different desired phases thereof by changing the discharge tube light emission phase with respect to vocal cord vibration.
Furthermore, it is also possible to observe the vocal cords gradually moving, or the vocal cords in slow motion, by automatically, continuously and gradually changing the phase. Hereinafter, where the discharge tube emits light in phase with vocal cord vibrations, the range in which the phase can change will be referred to as "a phase shift range" when applicable.
A conventional larynx stroboscope device is disadvantageous in that the phase shift range can greatly change depending on the frequency of the vocal cord vibration. For instance, where the phase is changed by operating a foot-operated pedal, the phase is changed considerably by slightly changing the amount of pressure on the pedal when the vocal cord vibration frequency is high, when compared with the case where the vocal cord vibration frequency is low. Accordingly, it is difficult to precisely observe the vocal cords when the vocal cord vibration frequency is high.
Furthermore, with the conventional larynx stroboscope device, when the observer observes the vocal cords in slow motion, the phase shift range with respect to the vocal cord vibration obtained when the vocal cord vibration frequency is low is very different from that obtained when the vocal cord vibration frequency is high. The time required for the phase to complete its change in the phase shift range is independent of the vocal cord vibration frequency. Therefore, if a rate at which the phase changes is referred to as "a phase shift rate", then the phase shift rate changes depending on the vocal cord vibration frequency. In other words, if the vocal cord vibration frequency of a person to be examined is changed when his vocal cords are observed in slow motion, the speed of the slow motion is accordingly, changed, and therefore it is difficult to observe the vocal cords.